package com.sakura.java8.lambda;

import com.sakura.java8.lambda.pojo.Employee;
import org.junit.Test;

import java.io.PrintStream;
import java.util.Comparator;
import java.util.function.*;

/**
 * 一、方法引用：若 Lambda 体中的功能，已经有方法提供了实现，可以使用方法引用
 * （可以将方法引用理解为 Lambda 表达式的另外一种表现形式）
 * <p>
 * 1. 对象的引用 :: 实例方法名
 * <p>
 * 2. 类名 :: 静态方法名
 * <p>
 * 3. 类名 :: 实例方法名
 * <p>
 * 注意：
 * ①方法引用所引用的方法的参数列表与返回值类型，需要与函数式接口中抽象方法的参数列表和返回值类型保持一致！
 * ②若Lambda 的参数列表的第一个参数，是实例方法的调用者，第二个参数(或无参)是实例方法的参数时，格式： ClassName::MethodName
 * <p>
 * 二、构造器引用 :构造器的参数列表，需要与函数式接口中参数列表保持一致！
 * <p>
 * 1. 类名 :: new
 * <p>
 * 三、数组引用
 * <p>
 * 类型[] :: new;
 *
 * @Author Sakura
 * @Date 2022/11/7 16:19
 * @Version 1.0
 */
public class LeaarnMethodRef {


    //对象的引用 :: 实例方法名
    @Test
    public void test1() {
        PrintStream ps = System.out;
        Consumer<String> con = (str) -> ps.println(str);
        con.accept("Hello World！");

        System.out.println("--------------------------------");

        Consumer<String> con2 = ps::println;
        con2.accept("Hello Java8！");

        System.out.println("--------------------------------");

        Consumer<String> con3 = System.out::println;
        con3.accept("我草！");
    }

    @Test
    public void test2() {
        Employee emp = new Employee(101, "张三", 18, 9999.99);

        Supplier<String> sup = () -> emp.getName();
        System.out.println(sup.get());

        System.out.println("----------------------------------");

        Supplier<String> sup2 = emp::getName;
        System.out.println(sup2.get());

    }

    // 类名 :: 静态方法名
    @Test
    public void test3() {
        BiFunction<Double, Double, Double> fun = (x, y) -> Math.max(x, y);
        System.out.println(fun.apply(1.5, 22.2));

        System.out.println("--------------------------------------------------");

        BiFunction<Double, Double, Double> fun2 = Math::max;
        System.out.println(fun2.apply(1.2, 1.5));
    }

    @Test
    public void test4() {
        Comparator<Integer> com = (x, y) -> Integer.compare(x, y);

        System.out.println("-------------------------------------");

        Comparator<Integer> com2 = Integer::compare;
    }

    //类名 :: 实例方法名
    @Test
    public void test5() {
        BiPredicate<String, String> bp = (x, y) -> x.equals(y);
        System.out.println(bp.test("abcde", "abcde"));

        System.out.println("-----------------------------------------");

        BiPredicate<String, String> bp2 = String::equals;
        System.out.println(bp2.test("abc", "abc"));

        System.out.println("-----------------------------------------");


        Function<Employee, String> fun = (e) -> e.show();
        System.out.println(fun.apply(new Employee()));

        System.out.println("-----------------------------------------");

        Function<Employee, String> fun2 = Employee::show;
        System.out.println(fun2.apply(new Employee()));

    }


    //构造器引用
    @Test
    public void test7() {
        //根据参数列表匹配，构造器
        Supplier<Employee> sup = () -> new Employee(1, "哈哈", 12, 345);
        System.out.println(sup.get());

        Supplier<Employee> sup2 = Employee::new;
        System.out.println(sup2.get());

        System.out.println("``````````````````````````````````````````````````````````````");

        Function<Integer, Employee> fun = (x) -> new Employee(x);
        System.out.println(fun.apply(8));
        Function<Integer, Employee> fun2 = Employee::new;
        System.out.println(fun2.apply(3));
    }

    //数组引用
    @Test
    public void test8() {
        Function<Integer, String[]> fun = (args) -> new String[args];
        String[] strs = fun.apply(10);
        System.out.println(strs.length);

        System.out.println("--------------------------");

        Function<Integer, Employee[]> fun2 = Employee[]::new;
        Employee[] emps = fun2.apply(20);
        System.out.println(emps.length);

    }

}
